The invention relates to heat exchanger elements and more particularly to hollow shapes for heat exchangers, a tube bundle comprising one or more hollow shapes and a procedure for manufacturing such hollow shapes and tube bundle. The specially designed hollow shapes are integrally extruded and each comprises a number of tubes and a plurality of thin interconnecting webs or lamellae between and connecting the adjacent tubes.
Heat exchangers comprising a plurality of parallel tubes projecting into headers and forming a heat exchanger unit (element) are at present mainly made of aluminum or copper tubes with interjacent lamellae which are mutually connected in order to establish a heat-conducting connection.
The connection between tubes and lamellae can be obtained by soldering/brazing or welding, and to facilitate this operation the tubes or lamellae are plated with, e.g., AlSi alloy which during a subsequent heating of the assembled heat exchanger melts, thereby ensuring a reliable, firm connection.
In the case of heat exchangers which are made up of flat or flat oval tubes, brazing or soldering has until now been the only possible connection method. When using tubes with a circular cross-section, a simplified connnection method has been established. Here the heat exchanger is assembled using specially formed top and bottom headers, after which the tubes are given a permanent deformation mechanically or under pressure, by expansion against the limiting lamella sides.
Such an assembly method is however not possible in the case of flat, oval tubes, as these cannot maintain the contact pressure against the lamellae over the entire circumference.
Soldering or brazing of the individual tubes is however a highly labour-intensive and cost-adding operation, and although using expansion of the individual tubes does not result in a connection of the same quality and strength, something which reduces the efficiency of the heat exchanger, it is nevertheless this later method which is presently primarily used in the manufacture of heat exchangers.